The invention relates to an apparatus for embedding a ticket signal in an analog video signal that has been obtained from converting a copy protected digital video signal into the analog domain, to a method for embedding the ticket signal in the analog video signal, to an analog video signal provided with the ticket, such that it will be removed or distorted when recording the analog video signal provided with the ticket on an analog VCR and subsequently reproducing the analog video signal therefrom, but does not distort normal reproduction of the analog video signal from that analog VCR, as well as to a record carrier provided with the video signal with the embedded ticket signal.
Prior art copy protection schemes are eg. the well known Macrovision copy protection method in which a selected waveform is added to the blanking interval of an analog video signal in order to prohibit recording and subsequent reproduction on/from an analog VCR. Reference is made in this respect to EP 256,753. Further, reference is made to EP 328,141, which discloses a what is called xe2x80x98serial copy management systemxe2x80x99, which enables a restricted number (n) of copies to be made from the original or from a subsequent copy. The original material includes a count value representative of the value n. During a subsequent copy made from the original or from a copy, the count value included in the copied material is decreased by one, until the count value reaches the zero value, which subsequently blocks the making of further copies.
The proposed standard-specifications for new digital video media such as DVD-RAM (DVD=Digital Video/Versatile Disk) and possibly also VDR (Video Disc Recorder) will be endowed with a copy-protection mechanism. The schemes implement besides the obvious xe2x80x9ccopy-neverxe2x80x9d or xe2x80x9cfree-copyxe2x80x9d, the third xe2x80x9ccopy-oncexe2x80x9d/xe2x80x9ccopy no morexe2x80x9d category of content. The latter possibility enables consumers to make a single copy of xe2x80x9ccopy-oncexe2x80x9d content, e.g. for back-up or time-shifting purposes. xe2x80x9cCopy-once/copy-no morexe2x80x9d is also required to comply with legislation in some regions of the world. The copied version receives the copy status xe2x80x9ccopy-no-morexe2x80x9d.
The basic copyright information is carried by embedding a watermark in the video content (in its most basic form slight alterations of luminance of predetermined pixels in the video material: invisible to the eye, but easily detectable in a playback device). There will be a different watermark for every one of the 3 copy categories. A watermark should be designed to be robust against a plethora of transformations: i.e. the watermark should still be detectable after basic image-processing (aperture filtering, 4:3⇄16:9 conversion, NTSC⇄PAL, letterboxing, digitalxe2x86x92analogxe2x86x92digital), but also after serious hacking attempts. The watermark is a secret, only known to the embedder (the provider of the video-material).
In the case that the watermark describes the content as xe2x80x9ccopy-oncexe2x80x9d/xe2x80x9ccopy no morexe2x80x9d, some additional signal in the video stream ought to indicate which of the two generations: xe2x80x98copy-oncexe2x80x99 or xe2x80x98copy no morexe2x80x99 describes the underlying video. Contrary to the watermark this signal should be changed in consumer devices in the process of copying. To accommodate this, various schemes have been proposed, introducing the so-called xe2x80x9cticketxe2x80x9d concept The ticket consists of 64-bits which indicate whether a given disc/tape is the original (copy-once), or a recording of the original (copy no-more), that can no longer by copied by devices which adhere to the copy-protection rules. Of course this information could be encoded in just 1 bit, such with SCMS/CGMS copy-management rules, but this would make it also very easy for pirates to hack. Rather one chooses to relate 64 bits cryptographically to the underlying content. The number xe2x80x9c64xe2x80x9d is essentially dictated by the amount of effort required to xe2x80x98crackxe2x80x99 the cryptographic algorithm by brute force.
Beside the (future) players/recorders that adhere to this copyright information, the so-called xe2x80x98compliantxe2x80x99 recorders, there are those in the xe2x80x98non-compliantxe2x80x99 world: machines modified by hackers, but also the enormous extant base of analog VCRs. Because one of the requirements of a copy-protection mechanism is backwards compatibility, we should allow VCRs (operating under the specifications of formats such as VHS, Beta, Video-8, S-VHS, Hi-8 etc.) to be able to record xe2x80x98copy-oncexe2x80x99 material. After copying, we want the video content now to be xe2x80x98copy-no morexe2x80x99. Compliant recorders should not be able to make a 3rd generation copy. Consequently, the ticket T should be designed in such a way that it is automatically stripped by these existing non-compliant recorders.
The objective thus is that analog video is recorded on tape together with the ticket, on a VCR which knows nothing about copy-protection. During playback of the tape, the analog video should reappear, but the ticket should be absent from it, see FIG. 1.
It is therefore the purpose of the invention to propose a number of low bit-rate information channels in an analog CVBS (Composite Video Blanking/Synchronization) signal of either NTSC-, PAL- or SECAM-signature, which are automatically removed upon recording or playback using analog consumer-grade VCRs. It would be desirable if the ticket would not get removed until playback, ie. in FIG. 1, removal takes place in VCR(OUT) rather than VCR(IN). Otherwise, future compliant analog VCRs would not be able to play xe2x80x98copy no morexe2x80x99 tapes: once they detect a watermark claiming xe2x80x9ccopy-oncexe2x80x9d/xe2x80x9ccopy no morexe2x80x9d status, they interpret absence of a ticket as a hack and their playback is stopped.